1. Field of the Invention
Exemplary embodiments of the present invention relate to inverse quantization of an image, and more particularly, to method and apparatus for inverse quantizing an image capable of reducing quantization error during decoding of an image and a method and apparatus for decoding an image using the method and apparatus for inverse quantizing an image.
2. Description of the Related Art
Generally, in the video compression standards such as Moving Picture Expert Group (MPEG) and H.26X, image data is compressed through operations including predicting image data, transforming the image data, quantizing the image data, and encoding the image data, thereby generating a bitstream.
In the predicting operation, a prediction image of the image data to be encoded is generated through intra-prediction using spatial correlation of the image or inter-prediction using temporal correlation of the image.
In the transforming operation, error data, which is the difference between the prediction image generated in the predicting operation and an original image, is transformed into a transform domain using various transforming methods. Examples of the transforming methods include Discrete Cosine Transform (DCT) and wavelet transform, etc.
In the quantizing operation, transformation coefficients generated by the transforming operation are appropriately lossy-compressed according to a size of the target bitstream. Most standard images and video codecs based on lossy compression perform quantizing and inverse quantizing operations by employing a quantization step. In the quantizing, an input value is divided by the quantization step and is rounded to integer so as to obtain a quantized value. Since the quantized value becomes an integer within a range of 1/(quantization step) from an original range of the input value, information is lossy-compressed through the quantizing operation. All lossy compression technologies include the quantizing operation such that original data cannot be restored completely but compression ratio may be increased.
When quantization is applied and thereafter, the encoded image is decoded, the quantization step is multiplied by the quantized value so as to perform inverse quantization. The quantized value becomes an integer within a range of 1/(quantization step) from a range of an original value so that an error known as a quantization error may be generated between an inverse quantized value and the original value.